int Conta;

void Calc_c (double *mat_a, double *mat_b, int l1, int l2)
   {
      int i, j;

      Conta++;

      for ( i = 0; i < l1; i++ )
         for ( j = 0; j < l2; j++)
             mat_a[i+j*l1] = mat_a[i+j*l1] + mat_b[i+j*l1];
/*            mat_a[i][j] = mat_a[i][j] + mat_b[i][j]; */
   }